A spray metering pump suitable for use on a receptacle that is under pressure is known in the prior art. It is described in greater detail with reference to the sole accompanying figure. Several variants can be found in French patent application No. 2 620 052 filed in 1987 by Valois. For the time being, it is merely specified that there is nothing to prevent this pump from operating when the pressure inside the receptacle has fallen to atmospheric pressure. In other words, in the event of gas leaking from the receptacle and a certain amount of air taking its place, there is a risk of administering a liquid that is unsuitable.
Thus an object of the present invention is to modify the prior art metering pump so as to make spraying impossible in the event of gas leaking from the receptacle.